When I switched hosts.... I had to move my .com address and during the transition we used .net.
Well after the conversion and I switched everything over to .com, my users had nightmares.... it seems the cookies from .com and .net are different.
All was fixed on our end by having the users trash their cookies. But before they did that, they could not remain logged in.
Also... make sure it's using the same domain everywhere. Watch the URL bar. If it changes to a different domain, you won't have the cookie anymore.
I ultimately had to set up a redirect so that anyone still using the .net address of mine would get switched to .com before they started on threads.... because it didn't like using it under 2 domains.
Hope that helps!
